The “Software Tools for Morphological and Syntactic Analysis of natural Language
Texts” is a software system designed for natural language texts processing. The
language texts. Specific formalisms has been worked out for this purpose allow us to
write down syntactic and morphological rules defined by particular natural language
grammar [1]. These formalisms represent a new, complex approach that solves some
of the problems connected with the natural language processing. A software system
has been implemented according to these formalisms. Syntactic analysis of sentences
and morphological analysis of word-forms can be done within this software system.
Several special algorithms were designed for this system. Using formalisms described
parsing tree that describes relations between the individual words within the sentence,
and to collect all important information about the input sentence that was figured out
during the analysis process. It is necessary to provide a grammar file to the syntactic
analyzer. There must be written syntactic rules of particular natural language
grammar in that file. Syntactic analyzer also needs information about the grammar
categories of the word-forms of natural language. Information about the grammar
categories of the word-forms are used during the analysis process. However it may be
quite difficult to include all of the word-forms from the natural language into a
dictionary file. To avoid this problem, and to reduce size of dictionary file,
morphological analyzer is used. Morphological analyzer uses a dictionary file of
unchanged parts of words. Therefore this file will be considerably smaller, because
many word-forms can be produced by single unchanged part of word. The
morphological analyzer also needs its own grammar file. According to the specific
formalism, morphological rules of natural language must be written in that grammar
file. An input word is divided into the morphemes when applying these rules. And
important information about the grammar categories of word-form can be deduced
during the analysis.
An input sentence is passed to syntactic analyzer. Syntactic analyzer passes
each word from the sentence to the morphological analyzer. Morphological analyzer
will analyze the words according to the rules from the grammar file, using a
dictionary of words’ unchanged parts. After the successful analysis each word-form
will obtain information about its grammar categories, and this information will be
returned to the syntactic analyzer. At the end syntactic analyzer will try to parse the
sentence according to the rules from the syntax file.
Basic methods and algorithms, that were used to develop the system the, are:
operations defined on the feature structures, trace back algorithm (for morphological
analyzer), general syntactic parsing algorithm and feature constraints method. Feature
structures are widely used on all level of analysis. As an abstract data types they are
used to hold various information about dictionary entries. Each symbol defined in a
morphological or syntactic rule has an associated feature structure, which is initially
filled from the dictionary, or it is filled by the previous levels of analysis. Feature
structures and operations defined on them are used to build up feature constraints.
With general parsing algorithm it is possible to get a syntactic analysis of any
sentence defined by a context free grammar and simultaneously check feature
constraints that may be associated with grammatical rules. Feature constraints are
logical expressions composed by the operations that are defined on the feature
structures. Feature constraints can be attached to rules defined within a grammar file.
If the constraint is not satisfied during the analysis, then the current rule will be
rejected and the search process will go on. Feature constraints also can be attached to
morphological rules. However, unlike the syntactic rules, constraints can be attached
at any place within a morphological rule, not at the end only. This speeds up
morphological analysis, because constraints are checked as soon as they are met in the
rule, and incorrect word-form divisions into morphemes will be rejected in a timely
manner.
Formalisms that were developed for the syntactic and morphological
analyzers are highly comfortable for human. They have many constructions that make
it easier to write grammar files. Morphological analyzer has a built-in preprocessor,
which has a capability to process parameterized macro insertions.
The software system is written in C++ programming language standard. It
uses STL standard library. Program operates in UNIX and Windows operating
systems. Although the program could be compiled and used in any other platform as
well, which contains modern C++ compiler.
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